D3byEX 5.6: Ordinal Scale (Adapted to D3.js v4)
<!DOCTYPE html>
<html>
<meta charset=utf-8>
<head>
<meta name="description"
content="D3.js v4, .scaleOrdinal, ordinal scale" />
</head>
<body>
<script src="http://d3js.org/d3.v4.min.js"></script>
<script>
var colorScale = d3.scaleOrdinal() // v4
.domain(['red', 'green', 'blue'])
.range(['#ff0000', '#00ff00', '#0000ff']);
// view console: #ff0000 #00ff00 #0000ff
console.log(colorScale('red'), colorScale('green'), colorScale('blue'));
</script>
</body>
</html>